1. Field of the Invention
This invention concerns viscosity measurement in general. More specifically, it relates to a method and system for carrying out a viscosity measurement of lubricating oil to determine low temperature viscosity of engine oils at low shear stress.
2. Description of the Related Art
In testing the viscosity of oils at low temperature and low shear stress, it has been found that viscosity measurements at a chosen low temperature may give different values for different cooling cycles. Sometimes the viscosity may show a strong adverse response to certain types of cooling history. In this connection, engine oil pumpability is an important factor to determine in regard to lubricating oils. Because pumpability may vary with different additives, the testing procedure needs to determine such characteristics for individual oils and/or additives. However, the slow cool conditions involved in pumpability testing require substantial periods of time, e.g. on the order of two days for one cool down cycle. Consequently, testing a given sample for different cooling conditions takes an inordinate amount of time, especially so for running any substantial number of such tests.
There are two U.S. patents known to the applicants which deal with viscosity measurement, namely U.S. Pat. No. 1,870,412 H. T. Kennedy Aug. 9, 1932 and U.S. Pat. No. 3,798,960 J. R. Glass Mar. 26, 1974. However, the Kennedy patent subjects all of a plurality of samples to the same heating and/or cooling conditions so that each sample is subjected to only one cooling condition at a time. Consequently it is not relevant to the applicants invention.
The Glass patent discloses an automatic viscometer system. It makes use of capillary tubes for measuring the viscosity, and a given sample is subjected to unitary temperature conditions during a viscosity measurement. Consequently likewise, it is not relevant to the applicant's invention.
It is an object of this invention to provide a method and system for concurrently applying a plurality of cooling conditions or cycles to separate portions of a single sample to be tested. That is followed by measuring the viscosity of the whole sample including all of the cycles.
Another object of the invention is to provide for running a test cycle that includes a plurality of different test cooling conditions simultaneously. It ends with viscosity tests for all of said plurality of cooling cycles at relatively the same time.